The application of prefabricated technologies to be applied on the façades of existing buildings for their integrated seismic and energy renovation is becoming increasingly widespread. To this end, dedicated scan-to-BIM workflows need to be developed to create precise as-built representations of the building. This paper introduces an innovative methodology to transform point cloud data acquired through 3D laser scanning into precise 3D models of existing building envelopes, which can be seamlessly integrated into BIM environments for further analysis and modification. This methodology follows two distinct approaches depending on the presence of façade interruptions, such as balconies. It involves the systematic application of software tools, including CloudCompare to automate curve extraction from point clouds, and Rhinoceros to interpolate these curves into surfaces and solids, resulting in accurate as-built models. The generated geometric elements are then imported into a BIM environment as editable families, enabling comprehensive building information management. Beyond digital modeling, this approach provides essential data for the correct installation of prefabricated elements, ensuring their seamless integration with the new envelope with the existing structure and optimizing the overall performance of the renovated building. The methodology is validated through its application to a 1964 residential building in Catania. The validation process includes an accurate as-built survey of the existing façades and the definition of alignment planes for the installation of a new prefabricated wood-based envelope.